Well I've not done can kits for a while, but I do know that most brews will really taste a lot better by using all malt instead of dextrose. I'd look at an online calculator and figure out what you can do with the extracts. You can try BeerTools Beer Making Resources and Home Brewing Recipe Calculator and Formulator
for one I like.
Off the top of my head I'd definitely use 2 cans of extract in a 5 gal batch, maybe do 3 and no sugar at all, but that will bump your gravity up such that you'd probably need some more hop bitterness to even it out.
"People should not be afraid of their governments. Governments should be afraid of their people." - V
Secondary: Shady Lord RIS, Water to Barleywine, Pumpkin wine, burnt mead
Kegged: Crappy infected mild
Bottles: Apfelwein, 999 Barleywine, Oatmeal Stout, Robust Porter, Robust smoked porter, Simcoe Smash